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Australian weevils are battling Australian trees in the Florida wetlands

When an introduced species gets out of control, is it ever a good idea to introduce yet another species to fight it? New research says yes, writes Andrew Masterson.

The age-old battle of wood against weevil: the Oxiops vitiosa weevil was introduced to Florida’s Everglades to control melaleuca trees.

US Department of Agriculture

Given the plagues of cane toads and carp that ravage Australia’s native ecosystems, the thought of using one introduced species to control another would make most Australian ecologists shudder.

Research in the US, however, suggests precisely that strategy is what will eventually control one of the most pervasive and destructive plant species ever introduced into Florida’s Everglades region.

To add to the irony, both villain and the heroes of the story are Australian.

The villain is a species of tree known to all Aussies as the melaleuca (Melaleuca quinquenervia). It was introduced into southern Florida over 100 years ago and rapidly became established, competing successfully against native species and degrading the area’s freshwater ecosystems.

In 1997, trying to combat the melaleuca menace, the US Department of Agriculture (USDA) set loose a population of weevils (Oxiops vitiosa), which, in their native Australian habitat at least, feast on the trees and significantly weaken them in the process.

Now, 20 years later, a modelling exercise conducted by a team led by Bo Zhang of the University of Miami, suggests that the gamble is paying off.

Zhang and colleagues fed available data into a modelling platform known as the JABOWA-II Forest Simulator. They prepared scenarios for two separate freshwater environments – cypress swamps and bay swamps – then fed in different densities of melaleuca and native species remnants before adding in the weevil population.

Available information suggested that the weevil was already having a profound effect on the invading tree, with melaleuca growth dwindling by 83%. The longterm implications were unknown: would the Everglades return to prelapsarian health, or would the weevils make a desolation and call it peace?

After running the numbers, the team produced an optimistic conclusion. Although the weevils will never completely obliterate the melelauca, they predict the species will be reduced to a minimal presence, allowing native species to almost fully recover in around 30 years.

“This individual-based model is used for a lot of ecological research but this is the first time it was used to model the long-term effects of an invasive species,” says Zhang.

“Basically, it can simulate each individual tree inside a plot of land and this provides more detailed information about bio-control outcomes and, ultimately, what is the best outcome for the future.”

She adds that the model will be useful for predicting the success of other biological control attempts based on introducing exotic species.